Blocking layer rectifier



, or five hours.

treatment, the selenium softens so that the pres-v Patented Aug. 3, 1948 2,446,466 BLOCKING LAYER' nno'rmmn Stanley S. Fry, North Chicago,--Ill., assignor to Fansteel Metallurgical Corporation, North Chi- 1 cage, 11]., a corporation of New York No Drawing. Application November 11, 19 44, Sfil'ifll No. 563,104

12 Claims. (Cl. 175-366) This invention relates to blocking layer devices such as selenium rectifiers and light sensitive devices, and more specifically to means for forming an artificial blocking layer on the. selenium.

In the production of blocking layer devices hav-' ing a semi-conductor layer, for example, selenium rectifiers, a rigid carrier electrode or supporting electrode is provided with a thin coating or layer of selenium. The supporting electrode may be formed of nickel, nickel-plated iron, aluminum, magnesium, beryllium or other metals and alloys. A common practice in the production of selenium rectifiers includes grit blasting the iron disc or plate and electroplating the disc with nickel. The Purpose of the gritblasting is to present-a roughened surface to the selenium and to thereby improve the adherence of the selenium to the carrier electrode. The disc is then thoroughly cleaned and a thin film of selenium is applied over the nickel layer.

The selenium film or layer may be formed by a variety of methods. The plate 'or disc may be heated to a temperature above the melting point of selenium, for example, to a temperature of from 230 to 250 0., and the selenium in stick form may be rubbed across the heated plate in order to melt the selenium and form the desired film. Another method of application includes placing a measured quantity of powdered selenium or selenium in pellet form on the heated plate and flowing the melted selenium over the surface. The melted selenium is usually spread over the heated plate by mechanical means, as with a glass rod. The selenium may also be deposited on the carrier electrode from a vapor phase. The vaporization method is commonly employed in depositing the selenium film upon the light metal carrier electrodes. Various materials may be added to the selenium to increase its conductivity and otherwise impart desired characteristics and properties.

The selenium is then transformed into its gray crystalline state by heat treatment. The coated discs are generally stacked with mica, aluminum or other inert, smooth-surfaced discs or washers in contact with the selenium and between adjacent plates, and the stack subjected to a moderate pressure. The stacks under pressure are then subjected to a relatively low temperature. that is, to a temperature below 150 C.,'and maintained at such temperature for from one hour to four During this stage of the heat sure produces a layer of selenium of relatively uniform thickness and having a smooth surface.

The stacks are withdrawn from the oven or heat treating furnace and the plates are removed from the stack. The plates are then given a further heat treatment at a temperature approaching the melting point of selenium. This heat treatment is generally conducted at-temperatures between about 200 C. and the melting point of selenium, for example, about 210 C., for a period of from fifteen minutes to several hours. During the combined heat treatment, a layer of selenium is produced having a smooth surface of more or less uniform thickness and the selenium is transformed from its amorphous,

non-conducting form into its gray, crystalline,

conducting form.

The smooth surface of the selenium film is then treated to form an artificial blocking layer and a counter-electrode consisting of a relatively low melting point alloy is applied, as by spraying, over the selenium coating. Y

The final step in the manufacture of the rectifier plates consists of an electrical forming treatment. This treatment consists of subi ecting the plate to either an alternating or direct current until a high resistance is developed in the reverse direction. This step may consist of applying to the plate in the reverse direction a direct current. voltage below about 15 volts or a pulsating direct current starting with a low voltage of about 8 volts and gradually increasing the voltage to about 21 volts over a period of several hours.

In the use of an alternating current, it is necessary to include-in the circuit a current limiting resistor because one-half cycle flows in the forward direction of the rectifier plate. The voltage may be about 20 volts and the period required for forming is generally greater than that required when. a direct current is employed because only one-half cycle of the current flows in the reverse direction. 1

. Light sensitive devices of the blocking layer class are produced in a similar manner. A supporting electrode is provided with a thin film or layer of selenium in its gray, crystalline modification and an artificial blocking layer formed on the surface of the selenium. A second electrode is then applied over the treated surface of the selenium. This electrode may consist of a lightpermeable film of metal or a metal grid. The application of the light-permeable metal may be accomplished by any of the methods known to the art.

This invention is directed to a method of forming an artificial blocking layer on the film of selenium in the manufacture of blocking layer tain added materials to impart desired charac teristics and properties.

The principal object of this invention is to provide a method of forming an artificial blocking layer on the surface of the selenium layer.

Other objects and advantages of this invention will become apparent from the following description and claims.

The present invention contemplates subjecting the surface of the selenium layer in its gray, crystalline modification to the vapors produced by heating a-IlltlOSO p-naphthol in the atmosphere to a temperature 'at which vapors are evolved.

The specific details of the manufacturing process of the element are dependent upon the type of unit being made and the class of service for which it is designed. For purposes of illustration,

the production of selenium rectifier plates is described.

A carrier electrode consisting of a grit blasted, nickel-plated iron disc is provided with a layer or film of selenium in its gray; crystalline form by any of the aforementioned methods. The selenium may contain added materials to improve the conductivity, as is well known to the art. The selenium surface is then exposed to the hot vapors produced by heating a-nitroso B- naphthol to a temperature at which vapors are evolved. The period of exposure of the selenium surface to the vapors may vary from a few seconds to several minutes, I prefer to expose the plate to these vapors for from about five seconds to about fifteen seconds.

The a-l'litIOSO pmaphthol may be placed in an open container and heated to the required temperature. The plates are exposed individually to the vapors by manually or mechanically passing each plate over the open top of the container through the rising vapors. The plates may be placed upon an endless conveyor belt which passes through a chamber having an atmosphere of the vapors.

The counter-electrode is then applied as by spraying a low melting point alloy over the treated selenium surface. The rectifier plate is finally subjected to any of the desired electrical forming processes known to the art.

One of the methods commonly employed in grading and in evaluating the quality of selenium rectifier plates is the determination of the rectification ratio of the rectifier plates. This ratio is the ratio between the current new in the reverse direction and the current flow in the forward direction upon the application of a direct current voltage to' the plate in the reverse and forward directions. An ideal or theoretically perfect rectifier plate would have no leakage current fiow upon the application of a direct current voltage in the reverse direction andthe rectification ratio would be 0.

In order to compare the rectification ratio of rectifier plates made in accordance with my invention and rectifier plates made without the artificial blocking layer treatment of this inven-- tion, a group of nickel-plated iron discs, having an area of about 3 sq. cm., was provided with a layer of selenium in its gray, crystalline form. The discs were heated to a temperature of about 240 C. and selenium in stick form rubbed across the plate. The selenium was spread over the surface or the heated discs with a glass rod. The selenium employed in coating the discs was a normal grade selenium for rectifier manufacture to which had been added about 0.1% iron cesium bromide to improve the conductivity of the selenium. The plates were then stacked with mica discs covering the selenium layer and the stack placed under pressure. The stack was heated to a temperature below 150 C. for about 2 hours. The pressure was removed and the plates heated to about 210 C. and maintained at this temperature for about /2 hour. The group of plates was then divided into two series.

The discs of one series of plates were individually exposed for about 10 seconds to vapors formed by heating a-BltIOSO B-naphthol in an open vessel to a temperature of about 200 C. at which vapors are evolved. The discs of the other series were used as standard or control plates.

The discs were subsequently provided with a counterelectrode and subjected to the same electrical forming treatment.

A rectified direct current voltage of 1 volt was applied to the individual plates 01 each series in the reverse direction and in the forward direction and the current fiow was measured. The leakage current or reverse current fiow in the case of the standard or control plates averaged approximately 0.23 mllliampere and the forward current flow averaged approximately 0.19 ampere. The rectification ratio of the control plates at a voltage of 1 volt averaged 1:830.

In the case of the plates in which the selenium 'surface had been subjected to the a-nltroso flflow averaged approximately 0.97 ampere. The

. characteristics are quite apparent from the data.

It is obvious that the numerical values of the leakage current and the rectification ratios will difler with different size rectifier plates, with different samples oi selenium, with difierent applied voltages and with difierent additive agents contained in the selenium.

I claim:

1. The method of producing blocking layer devices which comprises providing a supporting electrode with a layer of gray, crystalline selenium, subjecting the surface of the selenium layer to the action of vapors produced by heating anitroso fl-naphthol to a temperature at which vapors are evolved and applying a counter-electrode over the treated selenium surface.

2. The method of producing blocking layer devices which comprises applying a layer of selenium to a supporting electrode, transforming the selenium into its gray, crystalline form, subjecting the surface of the selenium layer to the action of vapors produced by heating a-Illtl'OSO B-naphthol to a temperature at which vapors are evolved and applying a counter-electrode over the treated selenium surface.

3. The method of producing blocking layer devices which comprises applying a layer of selenilenium surface.

4. The method of producing selenium rectifier plates which comprises providing a supporting electrode with a layer of gray, crystalline selenium, subjecting the surface of the selenium layer to the action of vapors produced by heating anitroso fi-naphthol to a temperature at which vapors are evolved, applying a counter-electrode over the treated selenium surface and subjecting the composite unit to an electrical forming operation.

5. The method of producing selenium rectifier plates which comprises applying a layer of selenium .to a supporting electrode, transforming the selenium into its gray, crystalline form, passins the coated plate through the vapors produced by heating a-nitroso p-naph-thol to a temperature at which vapors are evolved, applying a counterelectrode over the treated selenium surface and subjecting the composite unit to 'an electrical forming operation.

6. In a method of producing blocking layer devices including a selenium layer, the step which comprises exposing the surface of the selenium layer to vapors produced by heating a-IfitIOSO naphthol .to a temperature at which vapors are evolved.

'7. In a method of producing selenium rectifier plates, the step which comprises subjecting the surface of the selenium to the action of vapors 6 produced by heating a-IlltlOSO p-naphthol to a temperature at which vapors .are evolved.

8. In a method of producing selenium rectifier plates, the step which comprises subjecting the selenium surface for from about five seconds to about fifteen seconds to the action of vapor produced by heating a-nitroso p-naphthol to a temperature at which vapors are evolved.

9. The method of forming an artificial blocking layer on blocking layer devices including a layer of selenium which comprises subjecting the surface of the selenium to the action of vapor produced by heating a-nitroso B-naphthol to a temperature at which vapors are evolved.

10. The method of forming an artificial blocking layer on the surface of the selenium layer in a selenium rectifier plate which comprises subjecting the surface of the selenium for from about five seconds to about fifteen seconds to the action of vapors produced by heating a-nitroso p-naphthol to a temperature at which vapors are evolved.

11. A blocking layer device comprising a supporting electrode, a layer of selenium on the electrode, the surface of the selenium being treated with vapors formed by heating a-nitroso fi-naphthol and a counter-electrode on the treated selenium surface. a

12. A selenium rectifier plate comprising a supporting electrode, a layer of selenium on the electrode, the surface of the selenium being treated with vapors formed by heating a-ni-troso B-naphthol and a counter-electrode over the treated selenium surface.

STANLEY S. FRY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,121,603 Lotz June 21 1938 2,193,598 Lotz Mar. 12, 1940 2,264,464 Van Geel Dec. 2 1941 2,361,969 Saslaw Nov; 7, 1944 2,362,545 Ellis et a1. Nov. 14, 1944 

